This disclosure relates generally to methods and apparatus for drilling a wellbore. More particularly, this application relates to stabilizing a drillstring in a wellbore.
In certain drilling applications, stabilizers are placed at intervals along a drillstring. Stabilizers generally include axial ribs, blades, fins, or other protrusions that maintain radial spacing between the drillstring and the wall of the wellbore. By maintaining this radial spacing, stabilizers act to, among other things, prevent differential sticking, reduce buckling, and aid in fluid circulation.
In order to maintain radial spacing while not inhibiting movement of the drillstring through the wellbore, stabilizers must be able to pass through the wellbore. Therefore, in certain embodiments, stabilizers are often sized to have a maximum outer diameter that is slightly less than the diameter of the drill bit. This condition is known as being “under-gauge.” Although stabilizers that are slightly under-gauge will not contact the wellbore wall when the drill string is centered in the wellbore, as the drillstring is rotated, an under-gauge stabilizer will contact the wellbore wall.
Conventional stabilizers also feature grooves between the axial blades that provide flow channels for drilling fluid moving through the annulus between the drillstring and the wellbore. These grooves, known as “waterways,” may be straight, curved, spiral, helical, or otherwise angled with respect to the centerline of the drillstring. In certain conditions, such as in horizontal wells, wellbore debris may settle and accumulate along the wellbore wall above the drill bit and stabilizers. This debris may build up below and/or above the stabilizers or in the waterways and inhibit the circulation of drilling fluid through the wellbore. To mitigate build-up of debris, the waterways are usually sized as large as feasible, preferably without edges or other asperities that may potentially capture debris flowing in the waterways.
Thus, there is a continuing need in the art for methods and apparatus for improved drillstring stabilizers that mitigate build-up of debris.